Numerous electronic systems include digital-to-analog conversion (DAC) circuits to convert sequences of digital data samples to an analog signal. This allows storage and/or manipulation (e.g., frequency-selective filtering, or general analysis) of the signals via a computer or processor, which operates on quantized signals in a discrete time domain. As a final or penultimate processing step, the signals may be converted to an analog signal by a DAC for use by another circuit, such as by an amplifier. Many such DAC circuits suffer from high power consumption. Typically, various elements of the circuit (e.g., the output nodes coupled to the output resistors) are biased to a voltage level to ensure the circuit elements remain in a desired operating range, for example, to provide a desired linear behavior, or to provide a desired maximum dynamic range of the analog output signal.
Bias signals may cause undesirable power consumption because they may consume electrical current while the system is in a quiescent state. Furthermore, when amplified, an analog signal containing bias currents may result in additional unnecessary power consumption through the amplification of the bias currents. In a transmitting device this may be particularly problematic due to frequent periods of inactivity in between transmissions, and due to high levels of amplification during transmission periods. Furthermore, many transmitting devices, such as mobile phones, laptops, and portable devices, operate on batteries, where high power consumption is undesirable.
Accordingly, there is a need for more power efficient digital-to-analog conversion circuits, particularly for transmitting devices.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.